The invention relates to the equipment for processing of polymers, and more specifically to injection moulding machines for moulding articles from thermoplastic polymeric materials.
The invention may be most efficiently used for moulding articles of up to 40 m.sup.3 in volume, such as glass container lids, electric plugs, sealing members and the like.
Known in the art is a machine for moulding articles of thermoplastic polymeric materials (cf. French Pat. Nos. 1541603, B 29, 1968). The machine comprises a plastication arrangement, an injection cylinder communicating with the plastication arrangement, moulds spaced along the periphery of a rotor and means for removing gates and articles from the moulds. Means for removing gates from the moulds comprises a harpoon having catches in the form of helical or annular grooves, indents, recesses and the like and provided with a reciprocatory drive.
In operation, the injection cylinder is transferred to the gate passage of the mould and injects melt into the cavity of the mould. After a short-time delay, the injection cylinder is retracted from the mould, the rotor is caused to rotate through a pre-set angle, and the above-described operation is repeated for the next mould. During subsequent rotations of the rotor, the moulds are cooled, gates are removed from the gate passages, the moulds are then opened (that is male dies are spaced apart from the female dies), and the articles are removed from the moulds.
The main disadvantage of this machine resides in inadequate reliability of removal of gates from the gate passages. During the removal of a gate, the harpoon penetrates it and, during the return stroke, withdraws the gate from the gate passage of the mould. This method of removing gates is only applicable to the processing of low-hardness materials such as polyethylene. The machine cannot be employed for processing harder materials, such as polycarbonates, polyamides, polyformaldehydes due to a short life of the harpoons.
Furthermore, even in processing materials of low hardness, the above-described method of removing gates restricts the productivity of the machine since with an increased productivity, the time for gate removal operation becomes shorter, and failures to remove a gate from the gate passage are more likely to occur thus resulting in increased amount of rejects and substantial lowering of the use factor of the machine.
Known in the art is another machine for moulding articles from thermoplastic polymeric materials. This machine comprises a plastication arrangement, injection cylinders communicating with the plastication arrangement and arranged along the periphery of a rotor which is embraced by a closed conveyor carrying moulds for feeding melts thereinto from the injection cylinders, means for removing gates from gate passages and means for removing articles from the moulds.
In this machine, means for removing gates from the gate passages of the moulds comprises a rotor having harpoons spaced along the periphery thereof and actuated by a cylindrical cam.
Means for removing articles from the moulds comprises a rotor having mechanisms for opening the moulds and removing articles therefrom, which are spaced along the rotor periphery.
In operation, polymeric material flows through the plastication arrangement and heated passages of the rotor to get into the injection cylinders. The melt is injected from the injection cylinders, through the gate passages of the moulds, into the mould cavities, and the moulds are then successively transferred by the closed conveyor through means for removing gates and means for removing articles which also comprise rotors.
Gates are removed in this machine also by means of harpoons in the manner similar to that described above, the operating conditions being, however, substantially better. Operating time for gate removal may be selected to be an optimum one for any productivity of the machine by making a desired number of rotor stations for gate removal. This machine cannot, however, be used for processing high-hardness materials also in view of short life of harpoons.